As a conventional collating machine in the prior art, there are a vertical collating machine carrying out sheet feeding from a plurality of sheet feeders which are arranged in a vertical direction and a horizontal collating machine carrying out sheet feeding from a plurality of sheet feeders which are arranged in a horizontal direction.
A conventional horizontal collating machine is occasionally a collating machine having respective sheet feeders provided with an imaging device for checking collation errors. In the horizontal collating machine, for each of the sheet feeders, images printed on sheets are photographed by the imaging device, the images captured are compared with reference images which were preliminarily recorded, and the presence of sheet feeding errors is determined based on the result of comparison.
JP 2000-158843 A discloses an example of this kind of horizontal collating machine. FIG. 7 illustrates a schematic constitution of the horizontal collating machine described in JP 2000-158843 A.
Referring to FIG. 7, the horizontal collating machine is provided with a plurality of sheet feeders A to F which are arranged in a horizontal direction, and glass windows (not illustrated) are arranged at the bottoms of sheet trays of the sheet feeders A to F. Light sources La to Lf and CCD cameras Ka to Kf are installed on the sheet trays through the glass windows. Thus, when lights from the light sources La to Lf are irradiated against the sheet stacks mounted on the sheet trays in the sheet feeders A to F, images which were printed in a predetermined area of the sheets are simultaneously photographed by the CCD cameras Ka to Kf.
The image data (not illustrated) acquired by the CCD) cameras Ka to Kf are inputted in an image processing device. In the image processing device, the image data are compared with reference image data stored beforehand, and sheet feeding errors (feeding operation of sheets with different printing, feeding operation of blank sheets, and the like) are checked. Then, when they are judged as correct sheets to be fed, the sheets Pa to Pf are discharged from the sheet feeders A to F. Then the sheets are conveyed on a feeding path T while the sheets are overlapped one another in order so as to be collated.
On the other hand, in a vertical collating machine, there exists also a need for realizing the check of collation errors by checking images printed on sheets to be collated, using imaging devices in like manner as the horizontal collating machine. Consequently, in a conventional technology, there exists a vertical collating machine which carries out the check of collation errors, by arranging illumination devices and CCD cameras nearby the sheet trays of respective sheet feeders and reading the images of sheets discharged from the sheet feeders.
However, since respective sheet feeders of a vertical collating machine are arranged in a vertical direction at the least possible space therebetween, there exists a little space nearby the sheet trays of the respective sheet feeders. Thus the provision of CCD cameras and the like in the space may cause a problem that they hinder charging new sheets to the sheet trays. In this case, in order to carry out the charging new sheets to the sheet trays as smoothly as possible, the illumination devices and CCD cameras are arranged at the discharge outlet side of sheets of the sheet feeders. In this constitution, however, when maintenance working such as the removal of stains in the illumination devices and CCD cameras is required, it is not easy to access these devices.